Synonyms of insidious

insidious

adjective

as in treacherous

formal causing harm in a way that is gradual or not easily noticed

Most people with this insidious disease have no idea that they are infected.

an insidious enemy

Related Words

• treacherous
• subtle
• false
• deceptive
• perfidious
• incorrect
• wrong
• misleading
• deceitful
• cunning
• specious
• delusive
• wily
• beguiling
• sneaky
• fallacious
• ambiguous
• devious
• perplexing
• trick
• underhanded
• crafty
• shady
• tricky
• sly
• artful
• subtile
• deceiving
• delusory
• fast
• fraudulent
• puzzling
• underhand
• distracting
• confounding
• sneaking
• inaccurate
• shifty
• slick
• artificial
• foxy
• mendacious
• guileful
• duplicitous
• deluding
• untrustworthy
• trickish
• bewildering
• lying
• dishonest
• untruthful
• evasive
• faithless
• spurious
• bogus
• crooked
• counterfeit
• hypocritical
• knavish
• fake
• phony
• circuitous
• sham
• feigned
• ambidextrous
• dissembling
• forged
• equivocal
• insincere
• double-dealing
• jive
• backhanded
• defrauding
• two-faced
• left-handed

Dissimilar Words

• direct
• plain
• outspoken
• frank
• open
• candid
• illuminating
• straight
• explanatory
• revealing
• revelatory
• clarifying
• free-spoken
• truthful
• openhearted
• plainspoken
• honest
• elucidative
• trustworthy
• foursquare
• straightforward
• forthright
• aboveboard
• nondeceptive

Example Sentences

Recent Examples of insidious

But, as Ellis demonstrates in this survey of the city’s racial history, liberal policy achievements tend to obscure more insidious forms of exclusion. — The New Yorker, New Yorker, 20 July 2026

Beneath all the splendor, the couture, the balls, and the opera lurked an undercurrent of hatred, one that would fester and erupt in ways both insidious and catastrophic. — Literary Hub, 17 July 2026

But this last year, in particular, has broken new, insidious ground. — Los Angeles Times, 16 July 2026

In my view, statements to that effect are shortsighted, prioritizing short-term social effects over more insidious and long-term issues, including addiction. — Emma Fenske, The Conversation, 2 July 2026